SPARC/IO3C/GAW Report on Long-term Ozone Trends and Uncertainties in the Stratosphere

This Report summarises the main results obtained during the first year of the LOTUS activity, which was targeted at providing timely inputs to the 2018 WMO/UNEP Ozone Assessment. This deadline defined the scope of this Report and focused the LOTUS activities primarily on changes in ozone levels in the middle and the upper stratosphere outside the polar regions as observed by merged satellite records. These studies were complemented by an analysis of ground-based data and recent model data provided by the CCMI (Morgenstern et al., 2017). The short timeline of this work necessitated leaving several pressing topics for the second phase of LOTUS, most notably: the significance of recent trends in the lower stratosphere, the attribution of trends to ODSs and GHGs using model data, and estimates of trends in the polar regions.